1. Field of the Invention
This invention relates to the field of electrical activation of ion-implanted semiconductors. In particular, the invention relates to ion-implanted silicon in GaAs.
2. Description of the Related Art
The ion-implantation of semiconductors, and in particular the ion-implantation of silicon into GaAs, is an important doping technology for device fabrication. Particle accelerators accelerate silicon ions to impinge on and be implanted into GaAs. Implantation is followed by an annealing procedure which removes radiation induced damage and thermally transports dopants into lattice positions where they become electrically active. An activation of 100% is desirable, but in practice this is seldom achieved. For low fluences (from nil to .apprxeq. 5.times.10.sup.12 cm.sup.-2) various annealing techniques can result in activations of more than 80%, but at higher fluences percent activation generally decrease. At higher fluences on the order of 10.sup.14 cm.sup.-2, the reported activations vary widely and have been seen to depend strongly on the specifics of the post-implantation processing, including annealing.
The study of electrical activation of implanted dopants in GaAs as a function of implanted species, fluence and post-implant processing (annealing) has been an active research area in recent years. The ion-implantation process induces damage in the crystalline structure of the semiconductor. The annealing process reduces or ameliorates a portion of the induced damage. The study of implantation induced damage and its anneal characteristics has been ongoing for an even longer time than the study of electrical activation. Few of these studies report the dose rate with which the fluence was administered and there have been no studies reporting the impact of various dose rates on the electrical activation of the implanted species.
Japanese Patent No. 62-2533 to Ozawa discloses a method for obtaining sharp carrier concentration distributions by implanting silicon ions into an InGaAs layer at a specific accelerating voltage and at a specific dose after the ion-implantation is annealed. Ozawa discloses obtaining a peak carrier concentration of 7.5.times.10.sup.18 cm.sup.-3 when an accelerating voltage of 100 KeV is used with doses between 3.times.10.sup.13 cm.sup.-2 and 3.times.10.sup.14 cm.sup.-2 after the ion-implantation has been heat treated at 600.degree. to 700.degree. C. Ozawa does not disclose activation percentages or their dependency on implantation dose rates.
Japanese Patent No. 62-2532 to Ozawa disclosed a method for annealing an InGaAs ion-implanted dopant layer using a lamp furnace to enhance the activation of a conducting layer and to sharpen the carrier concentration distribution. Ozawa does not disclose the dependence of electrical activation on implantation dose rates.
U.S. Pat. No. 4,396,437 to Kwok et al. discloses a post-ion implantation annealing technique which involves applying an encapsulation over a device area capable of gettering a species that renders a substrate semi-insulating and then annealing the substrate to remove implantation damage resulting in high carrier mobility in an active region. The Kwok et al. patent does not disclose the dependence of electrical activation on implantation dose rates.
Japanese Patent No. 1-93115 to Tamura discloses a heat treating method to improve activation by applying an insulating film to one main surface of a semi-insulating GaAs substrate and then annealing the substrate before ion-implantation with SiF.sub.3.sup.+ improve the degree of activation. Tomura does not disclose the dependence of electrical activation on implantation dose rates.
U.S. Pat. No. 4,615,766 to Jackson et al. disclose a method of annealing ion-implanted doping impurities on at least one surface of a GaAs substrate by depositing a silicon capping layer after ion-implanting, and before annealing to remove damage to the substrate so as to prevent arsenic from evaporating from the substrate. Jackson et al. do not disclose the dependence of electrical activation on implantation dose rates.